Introduction To Information Technology

Remedial Class Notes

REMEDIAL CLASS NOTES CONTENTS COMPUTER CONCEPTS 1.0 Introduction 1.1 Objectives 1.2 Need for Computer Literacy 1

Prep. By MOHAMMAD DANISH (Lecturer , CSE Deptt.)

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Remedial Class Notes 1.3 Computer Capabilities 1.4 Computer Concepts 1.5 A Typical PC Characteristics 1.6 Question/ Answer Key

COMPUTER SYSTEM ORGANIZATION 2.0 Introduction 2.1 The System Concept 2.2 Organization of Computer System 2.2.1 Input Devices 2.2.2 Central Processing Unit (CPU) 2.2.3 Output Devices 2.3 Computer Limitation 2.4

Classification of Computers

2.5

Question/ Answer Key

SOFTWARE 3.0 Introduction 3.1 Software. 3.1.1 System Software 3.1.2 Application Software 3.2 Machine Language 3.3 Assembly Language 3.4 High Level Language 3.5 Question/ Answer Key

COURSE INTRODUCTION Computers are used in much application, like banking, military, medical instruments. In this course we are going to discuss the fundamental concept of computers, its working, how computer are useful for a society and its capability. How computers are classified, what is the relationship between software and hardware and what is the use of storage device and their capabilities are discussed. 2

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Remedial Class Notes Peripheral devices are responsible for carrying out input and output operations. The input devices include keyboard, mouse, light pen etc.. The output devices are printers, plotters and the monitors to name a few. Computer is an information process device, Hence devices for storing information are needed. Main memory holds programs and data. Main memory is volatile and limited in size. Secondary storage devices are nonvolatile and have sizes which are orders of magnitude more than the size of the main memory. Examples of secondary storage are hard disk, floppy disk, CD ROM computers store information in the digital form. In order to make a computer communicate with the analog world, a device called MODEM (Modulator Demodulator) is used. Modem converts the digital information to analog information for messages going out of a computer and vice-versa for incoming messages. Different computers might be equipped with different resources. For example a computer might have a printer attached and another. Computer might have useful programs. Sharing of resource will logically see that every computer will be able to use all the resources (whether available locally or not). Resource sharing becomes possible of the computer are connected together. LAN ( Local Area Network ) provide for resource sharing. In a network of computers programs are distributed on the different computers. A computer may have a program providing a certain service ( say printing ) running on it. It is useful to make the service available for requests coming from else where. Client/Server technology provides for service to be extended to request client request origination from any point of the network. Multimedia technology add multimedia capabilities ( audio, video) to a computer. A multimedia kit normally has a sound card, CD-ROM or DVD Drive and speakers.

COMPUTER CONCEPTS STRUCTURE 1.0 Introduction 1.1 Objectives 1.2 Need for Computer Literacy 1.3 Computer Capabilities 1.4 Computer Concepts 1.5 A Typical PC Characteristics 1.6 Question/ Answer Key

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Remedial Class Notes 1.0 INTRODUCTION No other technology has made such a rapid growth and change in science and technology in a short duration of time as the computer technology. Computers have a become a part and parcel of every human beings life. One can imagine the power and position of computers by looking into the statements " By the year 2099, there will be no clear distinction between humans and machines, we will have merged". Within the next 20 years, computers will be powerful like our human brain. Though computers by themselves have no intelligence and do not have the ability to learn, they have created situations that make us feel as if computers are better than human beings. In some ways, computers are fast, store large volumes of data and are more efficient than human beings. Computers are largely self-directing i.e. they have the ability to follow the set of instructions given to them ( of course, by human beings!)without human interaction. With limited intelligence, limited language capability (understands only programming languages) computers continue to dominate in the field of science and technology. The computers have emerged as a result of countless ideas inventions and developments made by different people throughout this century.

OBJECTIVES After studying this unit you should be able understand computer capabilities, functional blocks of a computer the difference between data and information, speed and accuracy capabilities. How data is manipulated.

NEED FOR COMPUTER LITERACY A few decades ago, a few computers in existence were very huge and expensive, they were usually used for scientific purposes and thus had little impact on the lives of common people; only a few people had the knowledge of computer capabilities and limitations. But over the period the scenario has changed. Millions of computers ranging from small micro-sized units to super-computers are found in offices, factories, schools, homes, hospitals, banks, retail stores and almost every where. Let us take a few examples and look at the use of computers 4

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Remedial Class Notes a) Travel arrangements for a trip: An efficient computer controlled airline reservations system keeps track of available seats and quickly records the reservation. b) You went to a hospital for physical checkup: If the exam is for insurance purposes, your medical history and the doctors finding will be forwarded to the insurance company where they are stored in a large computer data bank. c) Visit to a supermarket: When you go to a supermarket you can find several computers, which read the codes (like bar code) on the products and prepares the cash bills within a few minutes. There is no need for the customer to wait for a long time to get his bill. By looking at the typical sample examples listed above, the presence of computers in your daily life cannot be ignored or under estimated. Computers can have both good and bad effects on the individuals. Computer applications will expand greatly in the years to come. There will be vast potential for widespread benefits as well as undesirable side effects. Educated citizens should not rely solely on computer specialists to prevent the possible dangers and bring about the positive potential. Rather, citizens should learn about computers so that they can reap the benefits and they can insist the designers of ill-conceived computer systems to assume the responsibility for effects these systems have on people.

The following are the areas of knowledge required for computer literacy: 1. Computers themselves: You should understand the organization, capabilities and limitations of the various machines or hardware that make up a modern computer system. 2. What computers do: You should be familiar with some of the most common applications of computers in today's society. 3. How computers are put to work: You need to know the analysis, design and program preparation procedures that must be carried out in order to produce software. Basic knowledge of hardware is also very essential. 5

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Remedial Class Notes 4. The social impact of computers at work: Finally you should know how individuals and organizations may be affected by present and future computer applications.

COMPUTER CAPABILITIES Most people are aware that a computer is a machine that can perform arithmetic operations, but it is much more than just an arithmetic number crunching device. It is also a machine that can choose, copy, move compare and perform various non-arithmetic operations on many alphabetic, numeric and other symbols that humans use to represent things. The computer manipulates these symbols in the desired way through a sequence of instructions, called a program. A program is a detailed set of human instructions that directs the computer to function in a specific way to produce a desired result. Electrical or electromechanical components are known as hardware. a. Speed and accuracy capabilities: A computer works one step at a time. It can add, subtract, compare digits and, letters, move and copy numbers and letters. There's nothing profound in these operations. What's significant is the computer speed. This speed is measured as milliseconds, microseconds, nanoseconds and pico seconds (Recent study says computer speed is being doubled every six months). The speed required for computers to execute a basic operation like addition varies from a few microseconds for the smallest machines to 80 nano seconds or less for the larger ones. Thus, the slowest computers can perform hundreds of thousands of additions in a second while the largest systems can compute several million additions in the same period. In addition to being very fast, computers are also very accurate. It is estimated that you or I would make one error in every 500 to 1,000 operations with a calculator. But the circuits in a computer require no human interaction between processing operations and have no mechanical parts to wear out and malfunction. Thus these circuits can perform hundreds of thousands (or millions) or operations every second and can run errorless for hours and days together at a time. 6

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Remedial Class Notes Beyond this, computers also have built-in self-checking capabilities that permit them to monitor the accuracy of their internal operations. If the input data are correct and relevant, and if the program of processing the instructions is reliable, then the computer can generally be expected to produce accurate output. The phrase " Garbage in, Garbage-out" or GIGO is used often by people who work with computers to illustrate the importance of input data and correct instruction. b. Data manipulating capability: The first computers were built to manipulate numbers in order to solve arithmetic problems. Along with numbers we also use alphabets and different symbols in our daily life. Luckily, early computer experts made the important discovery that a machine that can accept, store and process numbers can also manipulate non-numeric symbols. Manipulating these familiar symbols is possible if an identifying code number is assigned to the symbol to be stored and processed. Thus, the letter A can be represented by a code, as can the letter B, the addition symbol and so on. Of course, one must give the computer instructions for it to manipulate the coded and stored symbols in a desired way. c. Data - versus - information: The word " data" is the plural of datum, which means fact. Data then, are facts or raw material of information. Data are represented by symbols. Information is data arranged in ordered or useful form. That is information is relevant knowledge produced as output of data processing operations and acquired by people to enhance understanding and to achieve specific goals. The following schematic representation shows you the processing of raw data to provide information: Data decisions Collection actions

Raw data input

Data processing

Information output

End user and

d. Data Processing activities: Data processing consists of gathering the raw data input, evaluating and bringing order to it and placing it in proper perspective so that useful information is produced. All data processing, whether done by hand or computer system consists or three basic 7

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Remedial Class Notes activities: capturing the input data, manipulating the data and managing the output results. i)

Capturing the input data:

Data must be originated in some form and verified for accuracy prior to further processing. They may initially be recorded on paper source documents and then converted into a machine - usable form processing or they may be captured directly in paperless machine-readable form. ii) Manipulating the data: One or more of the following operation may have to be performed on the data that is collected. 1. Classifying: Organizing items with like characteristics into groups or classes is called classifying. Data taken from a materiel stores sales bill for example, may be classified by product sold,

Sales department sales person, or any other

classification useful for store management. Classifying is usually accomplished by assigning pre-determined abbreviation codes to the items being arranged. The three types of codes used are numeric, alphabetic and alphanumeric. 2. Sorting: Usually its easier to work with data if they are arranged in a logical sequence. For example: include first to last, biggest to smallest oldest to newest. Arranging classified data in such a sequence is called sorting. 3. Calculating: Arithmetic manipulations of the data is called calculating. For example: In calculating a sales person's pay, the hours worked multiplied by the hourly wage rate gives the total earnings. Payroll deductions such as taxes are then calculated and subtracted from total earnings to arrive at the sales person's take-home pay. 4. Summarizing: Reducing masses of data to a more concise and usable form is called summarizing. Example: the general manager of a retail store is interested only in a summary of the total sales of each department. A summary report would give only total sales information. Department managers may want more detailed information such as

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Remedial Class Notes the total sales of each department broken down into sales by product type and by sales person. e. Managing the output results: Once the data have been captured and manipulated, one or more operations may be needed. i) Storing and retrieving: Retaining data for future reference in storing, storage media such as paper ( in sheet, punched card or punched tape form), microfilm, or magnatic disks and tapes are generally used. Recovering stored data and / or information is the retrieving activity. One slow approach is for people to search file cabinets. A much faster method is to use electronic enquiry devices that are connected directly to a computer and mass storage unit containing the data. ii)

Communicating and reproducing: Transferring data from one location or operation to another for use or for further processing is data communication a process that continues until information in a usable form, reaches the final user. Some times of course, its necessary to copy or duplicate data. This reproduction activity may be done by hand or by machine.

COMPUTER CONCEPTS There's nothing new about the data processing steps just stated above. They have been performed down through the ages, first by hand, then by machine assisted manual and electromechanical punched card methods and now by computers. The four functions which follow are all that a computer can perform but they also include most data processing steps: i)

Input / Output operation: A computer can accept data(input) from and supply processed data(output) to a wide range of input/ output devices. Such devices as keyboards and display screens make human - machine communication possible. Multiple output documents may be reproduced by printers.

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Remedial Class Notes ii)

Calculation operations: The circuits in a computer are designed to permit addition, subtraction, multiplication and division.

iii)

Logic/ Comparison operation: The computer also has the ability to perform certain logic operations.

For example, when two numbers

represented by the symbols A and B are compared, there are only 3 possible outcomes: 1) A is equal to B ( A=B); 2) A is greater than B (A>B) or 3) A is less than B (A
A is Compared With B A
A>B A=B

This comparison ability makes it possible to classify item A is having or not having the characteristic of B. This simple ability to compare is an important computer property because more sophisticated questions can be answered by using combinations of comparison decisions. iv)

Storage and retrieval operations: Both data and program instructions are stored internally in a computer. Storing both data and instructions in same memory is known as stored program concept or John Von Neumann Concept. And once stored, both may be quickly called or retrieved for use. The time required for data to be retrieved is measured in micro-or nanoseconds.

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Remedial Class Notes TYPICAL PC CHARACTERISTICS Some of the major characteristics of a typical personal computer are summarised below. This should give a glimpse of a desktop computer and introduce you to some of the terms used with personal computer. FEATURE TYPICAL BRIEF DESCRIPTION CPU type 8088, 80286, 80386, 80486, The CPU determines how Pentium-I, II, III much memory the system can address, what kind of software it can run, and how fast it can go Bus type PC Bus (8-bit ISA), AT Bus The bus determines what (16-bit ISA), Proprietary kind expansion circuit 32-bit Micro Channel, boards will work in the EISA, Local or VESA bus, machine. Most buses are PC-Card, PCI incompatible with the others (exception: EISA bus computers can use ISA cards), which makes it important that you know which kinds of boards you’re buying BIOS American Megatrends, Inc BIOS (Basic Input/Output manufacturer (AMI), IBM, Compaq, System) is the low-level Phoneix, Award system software that determines how compatible your computer is. CPU Speed 4.77 MHz (PC speed) upto Megahertz (MHz) is a 200 MHz rough measure of system speed. All other things being equal, a 10 MHz machine is faster than a 5 MHz machine. (All other things generally aren’t equal) Video board Monochrome Adapter The video board affects (MDA), Color/Graphics what kind of software you Adapter (CGA), Enhanced can run and how quickly Graphics Adapter (EGA), data can get on the screen. Video Graphics Array It can be easily changed, (VGA) 8514 Adapter, and the oldest PC can use Extended Graphics Array anything from a (XGA), Diamond Viper monochrome board up to a ATI Mach 32. VGA or 8514. Changing 11

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Remedial Class Notes video boards may require updating software to use those video boards. Video boards vary by the number of colors and pixels (the dots on the screen) that they can display. Most important in modern video boards, however, is whether they hold video data as a simple “Dumb frame buffer” which requires that the CPU must do all the video work, or contain circuitry that can help with the grunt work of graphical screens: boards like that are said to be “bitblitter” boards. Parallel port Unidirectional, Bi- The parallel port acts as directional, EPP (Enhanced the basic interface for Parallel Port) printers. In its simplest form, it’s unidirectional. More modern parallel ports may support bi-directional data flow, or may even support higher speeds of data transportation, known as an Enhanced Parallel Port, usually abbreviated EPP. Bi-directional parallel ports are more and more essential in order to support newer printers, which work their best when teamed with a bidirectional or, better, EPP port. Serial port UART 8250, 16450, 16550 The UART is the main chip around which a serial port or internal modem is built. The 16550 UART is the fastest of the lot, and is essential for high speed communications and communications in 12

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Remedial Class Notes

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Amount of memory

640K - whatever

System Clock / Calendar

Built on motherboard or added on expansion board.

Hard disk interface

ST506/412, ESDI, SCSI, IDE, EIDE

Hard disk encoding scheme

MFM, RLL, ARLL

Keyboard type

XT-type, AT-type

multitasking environments. There are several kinds of memory or RAM (Random Access Memory) conventional, extended, and expanded. They all solve different problems. Some software won’t run without a particular amount of one or more of these kinds of memory. Most PCs come with 64 or 128 MB of RAM. Again, not terribly important. Machines with built in clocks usually have DIS support to directly read from or modify the time and date. Others must run a separate program. What method does the hard disk controller (a circuit card in the system) use to talk to the hard disk? This affects speed and can be easily changed in most systems. Modern systems use IDE or SCSI; SCSI is preferable for its flexibility. How much data is squeezed on to the area on disk called a track? These methods are used to squeeze more data onto a hard disk, and can easily be changed. IBM originally put a keyboard control chip in the keyboard for the PC and XT. They moved it to the motherboard for the AT, so you’ve got to know which kind of keyboard interface you’ve got. Most

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Remedial Class Notes clone keyboards have a switch allowing them to swing both ways.

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Floppies supported

5.25 inch 360 K, 1.2MB, 720K (Unusual); 3.5 – inch 720K, 1.44 MB, 2.88MB

Number of expansion slots

3-10

Configuration method

Switches configuration (CMOS) memory

Number of interrupts (IRQ levels) supported Number of DMA (Direct Memory Access) channels supported Sound Card

8 or 16

SCSI host adapter

SCSI-I or SCSI-II single ended or differential; normal, fast, wide, or

4 or 8

8 or 16 bit FM, MIDI, and/or wavetable Audio interface

What kind of floppies will your machine support? This can be changed fairly easily. The more, the merrier. Many bit-name computers only sport three expansion slots; look instead for the eight-slot models. Computers won’t work until you tell them about themselves, or configure them. It’s done with either physical switches or software. Affects the number and type of expansion boards in a system. Affects the number and type of expansion boards in a system. Sound boards support music and sound reproduction on your PC, but music and sound are represented in either an 8bit or a 16-bit format. 16bit is better, but takes more space. The sounds are recorded and reproduced either with FM synthesis, MIDI control, or wavetables. Additionally, a sound card in combination with a CDROM can play music on your PC, with the right audio interface cable. SCSI is a kind of universal hardware interface that allows you to put hard

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Remedial Class Notes fast/wide

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LAN board

Ethernet, Token Ring and ARCNet

CD-ROM Drive

Spin speed (internal or external) SCSI, IDE or proprietary interface

disks, CD-ROMs, tape drives, optical drives, and scanners onto your machine with a minimum of hookup trouble. SCSI is still an evolving standard, but with many choices Most PCs don’t have SCSI, but most could benefit from adding SCSI; all you need is the SCSI host adapter board and some software. Local area networks (LANs) allow PCs to communicate with one another, share data and printers. Each PC on a LAN needs a LAN transceiver card, and there are three types: Ethernet, Token Ring, and ARCNet. Ethernet is the most common. Most businesses have LANs, and more and more homes are adding LANs as they acquire PCs. support CD-ROM disks, which can hold almost 700 MB of data. More and more software ships solely on CD-ROM, making this item a necessity. They vary largely by whether they’re internal or external, and how quickly they can transfer data to a PC. Transfer speeds range from 150K/s (“single spin”), 300K/s (“double spin”), 450 K/s (“triple spin”), to 600 K/s (“quad spin”), 900 K/s (“six speed”). 1200 K/s (“eight speed”, 1500 K/s (“ten speed”) CDROM interface either by

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Remedial Class Notes

Printer Control language

Epson codes, HPPCL (Laser jet commands) Post Script others.

way of IDE or a SCSI host adapter or by way of a proprietary adapter. Printer control languages tell your printer how to underline words, put pictures on the page, and change typefaces.

QUESTION/ ANSWER KEY 1.

A _____________________ is a fast and accurate electronic ( or data)

manipulating system that will accept and store input data, process them and produce output results. 2.

_________________________ are facts or informational raw materials

represented by symbols 3.

Arranging classified data in a predetermined sequence to facilitate

processing is called ______________________. 4.

The

word

"

data"

is

the

plural

of

datum

which

__________________.

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means

Remedial Class Notes Answers: 1. Computer

2. Data 3. Sorting 4. Fact

Mark True or False True 1. Electrical or electromechanical components are known as hardware. 2. A Program is considered as hardware 3. Keyboard is considered as output device

Answers: 1. True

2. False

3. False

COMPUTER SYSTEM ORGANIZATION STRUCTURE 2.0 Introduction 2.1 The System Concept 2.2 Organization of Computer System 2.2.1 Input Devices 2.2.2 Central Processing Unit (CPU) 2.2.3 Output Devices 2.3 Computer Limitation 1.1 Classification of Computers 1.2 Question/ Answer Key 17

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False

Remedial Class Notes INTRODUCTION Lets take a look at our computer definition. A computer is a fast and accurate symbol manipulating system that is organized to accept, store, process and produce results under the direction of a stored program of instructions. This section explains the computer is a system and how a computer system is organized. Organization of computers input devices, Keyboard, mouse and classification of Computers.

THE SYSTEM CONCEPT The system is a group of integrated parts that have the common purpose of achieving same objectives. The following characteristics are important: 1. A group of parts : A system has more than one element. A steel ball is not a system but it might be part of a bearing assembly that could be combined with other components to produce an irrigation system. 2. Integrated parts: A logical relationship must exist between the parts of a system, mechanical and electronic systems such as washing machines and video games have components that work together.

And a personal

management system may consist of integrated procedures for recruiting training and evaluating employees. 3. Common purpose of achieving objectives: The system is designed to accomplish one or more objectives; all system elements should be controlled so that the goal is achieved.

Totally automated systems have highly

controlled operations; systems operated by people sometimes get out of control. A computer is a group of integrated parts that have the common purpose of performing the operations called for in the program being executed it is also a system. Any system may be comprised of smaller systems or subsystems. A subsystem is a smaller system contained within a larger one.

The

component parts found in most computer system ex: printers are systems in a way and computers in small may be considered subsystems in larger super systems such as air traffic control system. 18

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Remedial Class Notes ORGANIZATION OF COMPUTER SYSTEM Input Devices

central processing unit

output devices

Fig. 1 Overview of Processing

The figure above shows the basic organization of computer system. The system included input, processing and output devices. Let us see each component of the system in more details. INPUT DEVICES Computer systems use many devices for input purposes. Some allow direct human/ machine communication. The keyboard of a workstation connected directly to or online to a computer: Devices that read data magnetically recorded on specially coated plastic tapes or floppy plastic disks are popular. Regardless of the type of device used, all are components for interpretation and communication between people and computer systems. There are few important input devices which we will learn in details. Keyboard: Is the most friendly input device through which data programs are keyed in and certain commands to software can be given from the keyboard. The keyboard consists key switches there is one key switch for each letter, symbol number etc. much like a typewriter when a key is pressed, the key switch is activated. The keyboard has an electronic circuit to determine which key has been pressed. Then the 8-bit binary code is generated and sent to the computers. The binary code may be an ASCII ( American Standard Code for Information Interchange), EBCDIC ( Extended Binary Coded - Decimal Interchange Code) or Hex code.

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Remedial Class Notes Keyboards are classified into two types depending on the number of keys present in them. a) Ordinary Keyboard: consists of 86 keys. b) Extended Keyboards: consists of 101 keys ( Windows ready )

Keyboards are of two types based on the fashion of data transfer. a) Serial Keyboard: It sends the data, bit by bit in a serial fashion and the computer converts the data into a parallel type. b) Parallel Keyboard: It sends the data as a byte in parallel form, the bits are sent simultaneously on different lines( wires). Mouse: A mouse is a graphical input device the term mouse is used because of its shape. The mouse has two or three buttons on its top. The function of each button is defined by the software. The mouse also has a small rotating ball at the bottom. When the mouse is moved on a rubber pad, the ball rolls whose movement is converted into an electrical signal and seat to the CPU on the CPU this movement is interpreted and displayed on the screen of the monitor (CRT) in the form of movement of the arrow mark . This movement of arrow mark is used to highlight the graphical index on the screen. When a desired command shown on the screen is approached by the arrow mark due to the movement of the ball in the mouse the click button is pressed to highlight the same.

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Remedial Class Notes

Fig. 3. Mouse

There are 2 methods by which a mouse is connected to a computer serial interface and parallel interface.

CENTRAL PROCESSING UNIT (CPU) The heart of any computer system is the CPU. Three main sections are generally located within computers of all sizes. a) The Primary Storage Section: This section is used for four purposes. 1. Data are fed into an input storage area where they are held until ready to be processed. 2. A working storage space that holds the data being processor and the intermediate results of such processing. 3. An output storage area holds the finished results of the processing operations until they can be released.

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Remedial Class Notes 4. In addition to these data-related purposes, the primary storage section, also certains program storage area that holds the processing instructions. In addition to primary memory storage or main memory section most computers also have secondary storage capabilities ( like hard disk, floppy disk ) b) The arithmetic – logic section: All calculations are performed and all comparisons (decisions) are made in the arithmetic – logic section of the unit are temporarily placed in a designated working storage area until needed at a later time data may thus move from primary storage to the secondary storage many times before the processing is finished. Once completed, the final results are released to an output storage section and from there to an output device. c) Control Section : The control section maintains order and directs the operation of the entire system. Although it does not perform any actual processing on the data, the control unit acts as a central nervous system for the other components of the computer. At the beginning of processing, the first program instruction is selected and fed into the control section from the program storage area. There it is interpreted, and from their signals are sent to other components to execute the necessary actions.

OUTPUT DEVICES Output devices:- Like the input devices, output devices are instruments of interpretation and communication between humans and the computer system. Printer is Considered as output device. All input/output and secondary storage units are sometimes called peripheral devices.

COMPUTER LIMITATIONS Computers although they are very useful, they have some limitations. 22

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Remedial Class Notes i) Programs must be reliable: As a machine, the computers does what it's programmed to do and nothing else. This doesn’t mean that it must be stupid clever programs can be written to direct the computers to store the results of previous decisions. But a seemingly flawless program that has operated without a problem for months can suddenly produce non-sense. A reliable program that’s supplied with incorrect data may also produce non-sense. ii) Application logic must be understood: The computer can only process applications which can be expressed in a finite number of steps leading to a previously defined goal. Each step must be specifically and clearly define, if the steps in the problem solution cannot be precisely stated, the job cannot be done. The computer may not be of much help to people in areas where qualitative material or evaluation is important. For example, The market decision may be of a qualitative nature because sales volume data may rest on future social, political, technological and economical events. However, the computer can let the manager know how the product will fare under assumed price, cost and sales volume condition. iii) Applications must be suitable: Writing programs is a human task it can be time consuming and expensive. Thus, non-recurring jobs are often not efficient areas for business data processing applications. Rather as a general rule its most economical to prepare business programs for largevolume, repetitive applications such as payrolls that will be used many times.

CLASSIFICATION OF COMPUTERS Computers are classified by the type of data they are designed to process. Data may be obtained either as a result of counting or through the use of same measuring instrument. Data that are obtained by counting are called discrete data, examples of discrete data are total number of students in a classroom. Data that must be obtained through measurement are called continuous data. For example, of continuos data are the speed of an automobile measure by speedometer or the temperature of a patient as measured by a thermometer. A digital computer is a counting device that operates on discrete data. It operates by directly counting members ( or digits ) that represent numerals, letters or other special 23

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Remedial Class Notes symbols. Just as digital watches directly count off the seconds and minutes in an hour, digital processors also count discrete values to achieve the desired output results. In contrast to digital processors, however, there are also analog machines that do not compute directly with numbers. They deal with variables that are measured along a continuo scale and are recorded to some predetermined degree of accuracy. Temperature for example may be measured to the nearest tenth of a degree on the Celsius scale, voltage may be measured to the nearest of hundredth of a volt. A service station petrol pump may contain analog processor. Analog computers may be accurate to within 0.1 percent of the correct value. But digital computers can obtain whatever degree of accuracy is required simply by calculating additional places to the right of the decimal point. For example; A pi(π ) has a value of 3.1416. Actually the true value of pi is 3.14159.... ( this number could go on for pages) Desirable features of analog and digital machines are sometimes combined to create a hybrid computing system in a hospital intensive-care unit, for example analog devices may measure a patients heart function, temperature and other vital signs. These measurements may then be convicted into members and supplied to a digital component in the system. Classification of computers based on their size, cost & configuration. In this category computers are classified as micro-computers, mini computers, main frame computers, home computers and super computers.

MICRO COMPUTERS: A Micro computer is the smallest general-purpose processing system that can execute program instructions to perform a wide variety of tasks. The important features of micro computers are: 1. Micro computers are known as home computers, personal computers, desktop computers and small business computers. 2. These are small, low-cost digital computer with a micro processor as its CPU, a memory unit an input device and an output device. 3. The word length of a micro-computer lies in the range of 8-32 bits. 4. CPU’s are in a single chip 24

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Remedial Class Notes 5. Storage capacity is small 6. Applications include general-purpose calculations, industrial control, office automation etc.

PERSONAL COMPUTERS (PC’S): Personal computers are micro-computers for general-purpose computations. These are classified as PC, PC/XT, PC/AT and super AT (or super micro) based on their cost and configuration. All these types contain a CPU, RAM, ROM, CRT display, Keyboard and secondary memory. Features: 1. PC is the simplest and cheapest type of computer and it uses an INTEL 8088 ( micro processor chip) as CPU, 640 KB, RAM, 8KB ROM ( ROM can be extended upto 64 KB) and floppy disk as secondary memory; processing speed of a PC lies in the range 1-5 MIPS ( micro-instructions per second ) 2. PC/XT ( Personal computer extended technology) contains hard disk, floppy disk drives ( 360/1.2 MB), Intel 8088 CPU, 640 KB RAM and 8 KB ROM. This is costlier than a PC because of the hard disk it contains. PC/XT is a single user system. Processing speed of a PC lies in the range 1-5 MIPS and hard disk capacity lies in the range 20-80 MB. 3. PC/AT (Personal computer advanced technology) contains. Intel 80286 as CPU, 640 KB RAM (expandable to 4 MB), 64 KB ROM (expandable to 128 KB), hard disk drive and floppy disk drive (360 KB/1.2 MB), its CPU is powerful than the CPU of PC/XT and four to five terminals can be connected to it to make it multiuser. Processing speed of PC/AT lies in the range 1-5 MIPS and hard disk capacity lies in the range 20-80 MB. 4. Super AT( or super micros) uses a 32-bit CPU, Intel 80386 & 80486. The RAM capacity of super macros lies in the range 2-8 MB in 80386 CPU can be extended upto 32 MB and in case of 80486 upto 64 MB. The hard disk capacity of super macro lies in the range 200 –800 MB. The processor speed of 80386 CPU lies in the range 3-5 MIPS and that of 80486 CPU is 12 MIPS to 25 MHz clock UNIX is used as operating system. 25

Prep. By MOHAMMAD DANISH (Lecturer , CSE Deptt.)

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Remedial Class Notes The processing speed of home computers and microcomputers for industrial control is less than 1 MIPS. Home computers are used for entertainment, basic education and home management and income tax calculation, investment analysis etc..

MINI COMPUTERS: The salient features are:1. The word length is 32 bits and their processing speed lies in the range 10-30 MIPS. 2. RAM capacity lies in the range 8 MB – 96 MB ( in same it can be extended upto 128-256 MB) 3. The hard disk capacity lies in the range 380 MB – 2GB ( gig bytes) 4. Most mini-computers use Motorola 68030 and 68040 CPU. The Minicomputers which are faster and more powerful than microcomputers can support upped 64 or even 100 terminals and some minicomputers are Uni. Processor and some others are multi processor systems. These are used for payroll preparation and scientific computation, multi-user and interactive applications in college universities research organizations, industries, sophisticated real time(industrial) control, interactive engineering design work etc..

Examples of mini computers are:

26



IBMAS/400/B60



VAX8842(VAX stands for Virtual address)



Extension - VAX computers are manufactured by Digital Data Corporation)



WIPRO S – 68030V & S-6833V built around 68030 CPU



WIPRO LANDMARK 860 ( a super mini) built around Intel i860CPU



HP 9000 series 800 ( super mini) built around Hewlett Pacard’s VLSI RISC processors

Prep. By MOHAMMAD DANISH (Lecturer , CSE Deptt.)

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Remedial Class Notes 

HCL magnum built around 68030 CPU and 68040 CPU.

MAIN-FRAME COMPUTERS:-

The mainframe computers are faster and more powerful than mini computers. These computers are used where large amount of data are to be processed or very complex calculations are to be made and these tasks are beyond the computing capacity of mini computers. The main features are : 

The word length may be 48, 60 or 64 bits.



Memory capacity range is 64-256 MB and hard disk capacity is 1000 MB – 10 GB or more.



Processing speed lies in the range 30-100 MIPS.

The mainframe computers are used in research organizations, large industries, business organizations, government organizations, banks and airline reservations etc.. Example: IBM 4300 series  IBM 308X series  Latest model IBM 3090 series  IBM 9000 series  HP 9000 series 8705/400  HP 9000 model 8705/300

SUPERCOMPUTERS: The salient features are: 27

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Remedial Class Notes 1. Their word length is 64-96 bits; memory capacity is 256 MB & more; hard disk capacity 1000 MB and more 2. Processing speed lies in the range of 400 MIPS – 10000 MIPS. In a single machine cycle tow 64 – bit data can be added Super computers are much faster and more powerful than mainframe computers. Super computers are specially designed to maximize the number of FLOPS ( Floating Point Operations Per Second). Their FLOPS rating is usually more than igiga flops per second. A super computer contains a number of CPU’s which operate in parallel and make it faster. They are used for massive data processing & solving very sophisticated problems. They are used for weather forecasting weapons research and development, rocket launching, seismology, atomic, nuclear and plasnia physics. Example: CRAY – X – MP/14, X-MP/24 & X-MP/48  CRAY – MP, CRAYZ, CRAY3, CRAY Y-MPC  ETA 10 ( Developed by control data Corporation )  SX – 2 (Developed by Nippon Electric Corporation, Japan)  SX – 3R ( 25.6 GIGA FLOPS )  HITACS – 300 ( 32 GIGA FLOPS, HITACHI MAKE )

2.5 QUESTION / ANSWER KEYS True 1. Digital Computer Operates on continuous data 2. Random access memory is secondary storage memory 3. Classification of computers done depending on size, cost and 28

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False

Remedial Class Notes Configuration. 4. CRAY XMP/14 is a minicomputer

Answers : 1. False

2. False

3. True

4. False

SOFTWARE STRUCTURE 3.0 Introduction 3.1 Software 3.1.1

System Software

3.1.2

Application Software

3.2 Machine Language 3.3 Assembly Language 3.4 High Level Language 3.5 Question/ Answer Key 29

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Remedial Class Notes INTRODUCTION Software is a set of instructions to perform a task. Hardware is an electrical or electromechanical components of a computer. Software and hardware plays an important role for a computer. This unit discusses software and types of languages used on a computer.

SOFTWARE Software is defined as a set of programs that activate the hardware of the computer. A program is nothing but as sequence of instructions where each instruction is a command given to the computer to perform a certain specified operation or given data. Software can be classified into two parts: 1. System Software 2. Application Software

SYSTEM SOFTWARE It is a collection of programs executed as needed to perform functions such as: i) Receiving and interpreting user commands. ii)

Entering and editing applications programs and storing them as files in secondary storage.

iii)

Controlling I/O units to receive input information and produce output results.

iv)

Translating programs from source from entered by the user into object from consisting of machine instructions.

v)

Linking and running user – written applications programs with standard routines that exist on the system.

The system software consists of operating system, assembler, compiler, interpreter, debugging programs, text editors etc..

APPLICATION SOFTWARE Application software is the software that has been written to processor perform a specific job.

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Remedial Class Notes Example: Word processing packages for processing and manipulating text, spreadsheet packages for calculating finances and data analysis, CAD for designing and drafting etc..

MACHINE LANGUAGE A computer understands information composed of only zeros and ones hence it uses binary digits for its operation. A program written in the form of 0’s and 1’s is called machine language program. There is a specific binary code for each instruction. For eg: to add the contents of register A and register B, the binary code is 10000000 for Intel 8085 microprocessors. The binary code for certain operations differs from computer to computer.

ASSEMBLY LANGUAGE Writing programs in machine language is very difficult, tiresome and boring job for a programmer, it is error phone. To solve this problem and to facilitate programmer easily understandable languages have been developed. Assembly language is one of them. Programs can easily be written in alphanumeric symbols instead of Zeros & Ones meaningful and easily remarkable symbols are selected for this purpose. Example: ADD, for addition, SUB for subtraction CMP for comparison. Such symbols are called mnemonics. A program written in mnemonics is called assembly language program.

Assembler A program which translates an assembly language program into a machine language program is called an assembler. Assembly language  Assembler  Machine language (Source Program)

(Object program)

Disadvantages 1. Programming is difficult and time consuming 2. The assembly language is machine oriented i.e the programmer must have the knowledge of the hardware of the computer

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Remedial Class Notes 3. The program written in assembly language for one computer cannot be run on another computer

HIGH LEVEL LANGUAGES A High level language is one which is expressed in terms of simple English like language. The instructions written in high level language are called statements. The statements more clearly resemble English Mathematics as compared to mnemonics. Example: BASIC, PASCAL, FORTRAN, COBOL, ALGOL, LISP, ADA, SNOBOL Advantages 1. They are easier to learn as compared to assembly languages. 2. They make programs easier and faster to write 3. Provide better documentation. 4. The programmers do not have limitations to use a single type of machine. 5. Programs are portable i.e. they will run on any computer Many high level languages have been developed, some are for general purpose and some for special purposes. Example: PASCAL, PL/1, ADA AND C are general purpose languages. COBOL is for business purposes PROLOG is for logical reasoning BASIC for new comers SNOBOL for text processing

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Remedial Class Notes SOURCE LANGUAGE AND OBJECT LANGUAGE

The language in which a programmer writes programs is called source language. It may be high-level or assembly language. The language in which the computer works is called object language or machine language.

COMPILER A program which translates high-level languages into a machine language program is called compiler. For example, WATFOR (FORTRAN compiler), TURBO PASCAL compiler.

INTERPRETER An interpreter is a program which translates statements of a high level language program into machine code. In translates one statement of the program at a time. It reads one statement of a highlevel language program translates it into machine code and executes it. Then it goes to the next statement.On the other hand a compiler translates the whole program into machine codeHigh –level Language

Compiler or Interpreter

(Source Program)

Machine language (Object program)

3.5 QUESTION/ ANSWER KEYS State True or False: 1. Machine language is one which is expressed in terms of 0's & 1's. 2. Assembly Language is one which is expressed in terms of mnemonics 3. Compiler is a software which converts machine language to high level Language. 4. Fortran is a low level language.

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Remedial Class Notes Answers : 1. True

2. True

3. False

4. False.

PRINTERS STRUCTURE 4.0 Introduction 4.1 Objectives 4.2 Printers 4.3 Types of Printers 4.4 Check your progress

INTRODUCTION This deals with computer hardware that are used for outputing data from a computer and it also introduces various types of printers.

OBJECTIVES The objectives of this unit are  To introduce computer hardware which forms the essential components of a computer system. 

Which provides hard copy of the output.

PRINTERS 34

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Remedial Class Notes One of the most convenient and useful methods by which the computer can deliver a hard copy is by means of printing. For the sake of convenience, the printer should have the ability to print alphabetic character, decimal digits, and common punctuation marks etc..

Functions of a Printer The printer receives data characters from the computer and prints the characters on the paper. In addition, the printer also receives control characters from the computer. These control characters are not printable characters. They convey some sort of control information to the printer ( bold, italic underline etc.). Some of the control characters widely used are: CR (Carriage Return) : Specifies that the pointer head carriage should return to the first print column. Any subsequent data character received will be printed starting from the first column. LF (Line Feed): informs the printer to skip one line on the paper. FF (Form Feed): Instructs the printer to skip the paper to the beginning of the next page or form. In addition to these the printer has to send acknowledging signal back to the computer indicating the status.

Basic characteristics of a printer:1. Speed: Specified as CPS ( Character Per Second ) or LPM ( Lines Per Minute ). It indicates how fast a printer works. 2. Quality: Specified as DRAFT, NLQ ( Near Letter Quality ) or LQP ( Letter Quality Printer). This give how good the shape of the printer character is. 3. Character Set: Indicates the total number of data characters and control characters recognized by the printer. The normal ASCII and EBCDIC. 4. Interface: Specifying whether the printer receiving characters from the computer in parallel form or in serial form. 5. Buffer size: Indicates how many data characters can be stacked in the printer buffer memory before printing. 6. Print size: Specified as character size and number of characters per line.

TYPES OF PRINTERS 35

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Remedial Class Notes There are several types of printers that are designed for different types of mechanisms based on the approach of printing and speed; printers may be classified as: 1. Character printers 2. Line printers 3. Page printers Printers are also classified as: 1. Impact printers and 2. Non-impact printers Impact printers: The printers which use the familiar type written approach of hammering a typeface against paper and inked ribbon are called impact printers. Non-impact printers: The printers which do not hit or impact a ribbon to print, are called non-impact printer such printer uses thermal, electrostatic, chemical and inkjet technologies. Character printers: This category of printers generally functions in the same way as a typewriter. There are many types of character printers some of them are: Daisy-wheel printers: In daisy–wheel printer the raised letters are attached at the ends of spokes of a wheel. A motor spins the wheel at a rapid rate. The wheel is rotated until the desired letter is in position over the paper and then solenoid-driven hammer hits the ‘spoke’ against the ribbon to print the letter. The daisy-wheel printers are impact printers. The advantages of the daisy-wheel printers are high print quality, interchangeable fonts and print speed upto 55 characters per second. However the print quality is not as good as that produced by the spinning golf ball.

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Remedial Class Notes

Fig 4.1 Daisy Wheel Printer

1. Spinning golf ball printers: This also function in the same way as a daisy-wheel printer. The main difference in the mechanism is that the entire character set is present as raised type around a sphere. The bottom of the sphere is connected to the motor drive mechanism. The ball can be easily shifted up or down, rotated and tilted until the character to be printed can be precisely positioned over the desired location on the paper. For printing the letter on the paper, the spinning golf ball is hit against the ribbon. The head is moved across the paper to print a string of characters. The advantages of spinning golf ball printers are excellent print quality and easy interchangeability of fonts. However, this type of printers posses some disadvantages too, i .e it is mechanically complicated and noisy mechanism. It has low speed about 14 character per second. 2. Line printers: Are most suitable for massive data with higher speed of printing:

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Remedial Class Notes

Fig. 4.2 Line Printer

Drum printers:A drum type printer consists of a rapidly spinning drum which has a complete raised character set constructed around it for each character position across the paper.

Fig 4.3 Printing Cylinder of a Drum Printer Each band contains all the possible characters, Magnetically driven hammers are provided in each character position to hit the paper and ribbon against the spinning drum 38

Prep. By MOHAMMAD DANISH (Lecturer , CSE Deptt.)

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Remedial Class Notes for printing the desired characters. An entire line of characters can be printed during each rotation of the drum. With the help of the drum printer upto 2000 lines/min can be printed. The quality of printing is not good and there is also high noise pollution. Drum printers are also called line printers. Chain printers: A rapidly moving chain called print chain is used in chain printers. Each link of the print chain is a character's font. For printing a character, a print hammer is located behind the paper. As the print chain rotates, the properly timed hammers strike the paper and the ribbon together against the desired character set several times on the chain, the speed of chain printers can be improved. Speed of chain printers reaches up to 2500 characters per minute. Dot-Matrix Impact printers: A dot-matrix printers each character as a pattern of dots. The print head comprises a matrix of tiny needles having seven rows with nine needles in each row. The tiny needles hammer out the characters in the form of patterns of tiny dots. The print needles are arranged in a vertical column so that characters are printed out one dot column at a time as the print head is moved across the line. The quality of the print is not so good. However the quality of printing can be improved by printing a line twice with the dots for the second printing offset slightly from those of the first. Print speed of dot matrix impact printers is max of 350 cps. Page printers: The page printers are non-impact printers having speeds over 20,000 lines per minute. The technique called Electro-photographic technique is developed from the paper copier technology. The important type of page printers are: 1.

Electromagnetic printers: The magnetic recording technique is used in this type of printers. A magnetic image of the matter to be printed is written on a drum surface. The surface of the drum is then passed through magnetic powder which adheres only to the charged areas. This powdered surface is now pressed

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Remedial Class Notes on to the paper to obtain the hard copy of the data.

Speeds of

electromagnetic printers upto 250 characters per second may be obtained. 2.

Electrostatic printers: In such printers, a paper coated with a non-conducting electric material which holds the charges of voltages are applied with writing heads, is used, The heads( or nibs) write dots on the paper as it passes. The paper is now passed through a toner which contains material with particles carrying an opposite charge to that of that of the paper written by the nibs. The particles adhere to the magnetized areas and form printed characters.

3.

Laser and xerographic printers: The principle of laser printers and xerographic printers, is almost the same, The image of the page to be printed in first formed on a photosensitive drum in the printer. Powdered ink or tones is applied to the surface of the drum. Now, the image from the drum is electrostatically transferred to the sheet of paper. The ink image on the paper is finally fused by heating process internally. In case of a laser printer, the image on the photosensitive drum is produced by a laser beam. The laser is swept backs and forth across the drum to produce an image in the same way as produced on a roaster scale CRT. The rotating mirror sweeps the laser beam across the rotating drum, With the help of a modulator controlled by a microcomputer, the laser beam is turned on or off to produce dots. After the image is inked and transferred to the paper, the drum gets cleaned and gets ready for the next page. The speeds of laser and xerographic printers are to the tune of 20,000 lines per minute. The quality of print is also good.

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Remedial Class Notes

Fig 4.4 Laser Printer

CHECK YOUR PROGRESS 1. Pick up the correct statements from the following: a) Typical speeds of drum printers may be in the range of 300 to 2000 lines per minute. b) Typical speeds of chain printers may be in the range of 400 to 2500 characters per minute. c) Typical speeds of page prints may be even more than 20,000 lines per minute. d) All the above. 2. Printers: a) are most commonly used o/p device b) are used to prepare permanent documents c) are of several types d) all the above 3. The impact printers use: a) Thermal technology b) Chemical technology c) Electrical technology d) None of the these 4. Drum printers is a: a) Line Printers 41

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Remedial Class Notes b) Letter Quality Printers c) Dot-Matrix Printers d) None- of the above 5.The primarily used computer device for obtaining the hard copy is: a) Line Printers b) CRT c) Keyboard d) None State whether the following statements are correct: 1. The daisy wheel printers are called non-impact printers 2. Line printers are impact printers 3. A printer produces a hard copy 4. Line printers print an entire line at a time 5. A Daisy wheel printer is character printer Answers: I 1(d)

2(d)

3(d)

4(a)

5(a)

II 1)False 2) True 3) True 4) True 5) True

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Remedial Class Notes

MEMORY STRUCTURE 5.0 Introduction 5.1 Objectives 5.2 Types of Memory 5.3 Accessing Methods 5.4 UPS 5.5 Check Your Progress

INTRODUCTION Memory of a computer deals with storage of information. The secondary storage devices, which retain information in the absence of electrical power, are also discussed.

OBJECTIVES •

To introduce devices for storing information ( Volatile and Non-volatile )

•

UPS provides the back up during power failure

TYPES OF MEMORY The memory is used for storing information. It is classified into two groups 1) Primary memory and 2) Secondary memory Primary memory: is generally termed as computer’s memory, the main memory. The primary or internal storage is a most essential part of all computers. The internal storage area is made up of several small storage areas called locations or cells. Each of these locations can store a fined number of bits called word length of that particular 43

Prep. By MOHAMMAD DANISH (Lecturer , CSE Deptt.)

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Remedial Class Notes storage unit. Each location or word has a built in and unique number assigned to it. This number which is used to identify the location, is called the address of the location. The primary memory actually functions when the computer operates and is present in the computer in two different forms RAM & ROM. Random Access Memory (RAM): The primary storage is generally referred to as random access memory (RAM) because one can select and use any location of this memory to directly store and retrieve data instructions. Every location of the memory is easily accessed and time taken in each case is same. The facility of read/write from a RAM chip entitles it to call read/write memory. When the power is switched off, the information stored in RAM is lost. Read Only Memory (ROM): In this memory storage information is permanently stored. The information contained in can only be read and not written fresh information into it. When power is switched off the information stored inside a ROM is not erased, ROM memories are also known as fieldstores, permanent stores or dead stores. Cache Memory: A very high speed memory used to increase the speed of processing is employed between CPU and main memory whose access time is close to the processing speed of the CPU. This type of memory is called a high-speed buffer or cache memory. However, cache memory is not addressable by the user of the computer system. Cache memory makes the main memory of the computer appear to be faster and larger than what it really is. The cache memory is normally very small due to its high cost of construction; cache memory improves the memory transfer rate and also increases the processor space.

ACCESSING METHODS The memory of a computer is not actually concentrated in one place, Storage devices are scattered throughout the machine. For instance, the operation registers are flip flop registers which are used in the arithmetic and control units of the computer. The storage devices are used to introduce information to the computer from the “ outside world” and to store results from the computer. The procedures for locating information may be divided into two classes: 1. Random access storage devices and 44

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Remedial Class Notes 2. Sequential access storage devices. A random access storage devices : is one in which any location in the device may be selected at random access to the information stored in direct and approximately equal access time is required for each location. A sequential access storage device: is one in which the arrival at the location desired may be preceded by sequencing through other locations, so that access time varies according to location. For example, If we try to read a word stored on a real of magnetic type and the piece of tape on which the word is stored is near the center of the reel, it is necessary to sequence through all the intervening tape before the word can be read. Another way to subdivide storage devices is according to whether they are static or dynamic A static storage: is one in which the information does not change position example flip flop, tape are of static storage devices. A dynamic storage: Devices are devices in which the information stored is continually changing position. Circulating register utilizing change coupled device ( CCD) delay lines are example of dynamic storage devices.

Sequentially Accessed Devices: Punched paper tape: The paper tapes normally 1 inch (2.54 cms) wide are available in rolls of different length. Data is coded on the paper tape in the form of punched hole combinations, The length of the tape may be kept as required by the user. The information is recorded as holes punched in rows across the width of the tape. Each row represents one character. The maximum numbers of holes per row is known as number of channels on the tape. An eight-channel tape is generally used in computers. A line of sprocket holes in the middle of the tape is provided for the purpose of feeding the tape through the tape punching and reading device. Disadvantages

45

i)

Less numbers of characters can only be stored.

ii)

The paper tape media gets easily torn. Prep. By MOHAMMAD DANISH (Lecturer , CSE Deptt.)

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Remedial Class Notes Advantages i)

Storage capacity of paper tape is unlimited

ii)

Cost per bit stored is very low

Magnetic tape: This is most popular storage device for large data that are sequentially accessed and processed magnetic tape is a half-inch (1.27-cm) wide plastic ribbon, which is coated on the side with an iron oxide material which can be magnetized. The tape ribbon is housed in a cassette. The computer tape can be erased and reused indefinitely. The stored data on the tape gets automatically erased as and when fresh data, is recorded in the same area of the tape. Recording of information: Information in binary, is recorded on the tape as invisible magnetized and non-magnetized spots on the iron oxide side of the tape. 0 of the binary is represented by a non-magnetized spot and 1 is represented by the magnetized spot on the tape. The tape is divided into horizontal rows called channels or tracks and into vertical columns called frames. Each character of the information is recorded per frame based on the code of the computer. Data transfer rate: The product of tape density and tape speed is known as the data transfer rate of the magnetic tape. The number of frames per inch length of the tape is called tape density. The tape density of a magnetic tape is expressed in characters per inch (CPI) or bytes per inch. The tape speed is measured in inches per sec. Data transfer rate of a magnetic tape may even exceed 1 million bytes per second. Advantages of magnetic storage: 1. The storage capacity of a magnetic tape is unlimited. 2. It possesses high data density 3. Its cost is much less than other data storage devices 4. Its rate of data transfer is high 5. It is very easy to handle magnetic tapes 6. It is very easy to transfer information from one place to another.

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Remedial Class Notes Draw-backs of magnetic tapes: 1. As magnetic tape is a sequential access devices, the data recorded on tape can not be addressed directly. The data item at the end of the tape will require abnormal access time because all the characters before the data item need by processed. This is why magnetic tape device is not found suitable in case data is frequently required to be accessed at random. 2. It is not possible to interpret, the stored data to know the content of the information. 3. Dust free environment is needed for magnetic tapes and the reel containers. a) Tape Cassettes: A high quality digital cassette similar in appearance to the home cassettes. b) Cartridges: The large cassette which contains long strips of magnetic tape is called cartridge. It is very convenient to mount the tape there is proper protection against dirt and contamination. Both cassettes and cartridges have low data transfer rate, i,e , less than 10,000 bytes/sec. Random access devices: Magnetic Disk: It is a thin, circular metal coated on both sides with a magnetic material similar to a gramophone record. A number of magnetic disks mounted about half-an-inch apart from each other on a central shaft which may rotate at speed of 2400 or more revolutions per minute (RPM), consists a disk pack. Magnetic disk packs are the most popular medium for direct access secondary storage. Information is stored on both sides of the disks except the upper surface of the top disk and lower surface of the lower disk. Each face of the disk is divided into a number of invisible concentric circles called tracks. A set of corresponding tracks in all the surfaces is called a cylinder. Each track is sub divided into sectors. Information is recorded on the tracks of a disk surface in the form of minute magnetic spots. The magnetized spot represents a 1-bit and non-magnetized spot represents a 0-bit.

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Remedial Class Notes The information stored on a disk can be read a number of items and reading operation is non-destructive. To write a new data, the previously stored data has to be erased. The storage capacity of a disk pack primarily depends on the number of disks it contains. The storage capacity also depends on the track per inch of surface and the number of bits per inch of track. Magnetic Drum: Magnetic drum is also a direct access storage device that can be used for both sequential and random processing. It is basically a cylinder with a magnetizable outer surface. A motor rotates the cylinder on its axis at a rapid speed but constant rate. The surface of the drum is divided onto a number of tracks upon which data is stored as magnetized spots similar to that of a disk. Data is stored on the magnetizable surface of the cylinder as minute magnetized spots arranged in binary form in the series of parallel circular tracks. Recording of data on the rotating drum and reading data from the drum is achieved by a set of secondary read/write heads positioned very near to the drum surface. Writing a new data on the drum erases the previously stored data simultaneously at that location. Data once recorded on the drum remains intact until it is erased. The drum rotates at a speed of few hundred to few thousand rotations per minute and its access times is fast. Random access is possible to select any particular track of the drum but once this track is identified, the data is recorded or retrieved sequentially. To reduce the access time, sometime heads are divided into two sets. Heads are positioned diametrically opposite i.e for a drum of 20 track 40 heads are provided. As compared to magnetic disks, data transfer rates are faster. Due to limited storage capacity, use of magnetic drum storage is on decline. Winchester Disk: Winchester disk are also used as a storage device. In this unit, disks are permanently housed and hermetically sealed in contamination free containers. The disks are coated with a special lubricant which minimizes the friction between the read/write heads and the disk surface .Computers using these sealed housings are said to employ Winchester technology. The Winchester technology enables greater precision of alignment, an increase in the number of tracks on the disk surface and a higher storage density per track. Winchester disks are fast and highly valuable and low priced compared with conventional hard disk drives. They are available in sizes varying form 5.25” to 14” in diameter and there capacities are 10,12 and 20 megabytes. Dual disk drive doubles the capacity. Winchester disks are used in large computers. 48

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Remedial Class Notes Floppy Disk: A floppy disk is a circular Mylar disk coated and magnetically sensitive film. Since the thickness of the Mylar disk is only a few thousandth of an inch it is named as floppy. The floppy diskette is coated with a magnetic material and enclosed in a protective jacket. The floppy disks are used for backup of files and to transfer files from one computer to another computer Floppy diskettes can be classified as Single and double sided. If only one side of the diskette is used to store information such a diskette is called as a single sided disk. If both the side of the diskette is used to store information such a diskette is called as a double-sided disk. The diskette surface is logically divided into a fixed number of tracks (concentric circles). Data can be read and written on the specified tracks and not in between the tracks. Each track is divided into a number of sectors. The number of sectors in a track depends on the size. Users label Write Protect notch

Manufacturers Labs

Clamping hole Index hole Head slot

Fig 5.1 Floppy Disk A read/write head contacts the disk through the head slot to read from or write to the disk. It is designed such that it can move both forward and backward. The outermost track is numbered as track 0. The subsequent tracks are numbered sequentially. The Index hole is used as a reference point to indicate the beginning of a track. There is a facility to use a diskette only for reading previously stored information and to prevent any attempt to write new information on it through the write protect notch. If this notch is open writing on the diskette is permitted. 49

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Remedial Class Notes Advantages of floppy disks are: 

They are very cheap compared with other storage



They greatly enhance the on-line storage capacity



They are also convenient off-line storage medium

 The floppy disks generally available in market are of 3½, 5¼ or 8inch diameter size.

UNINTERRUPTED POWER SUPPLY (UPS) An Uninterrupted Power Supply is a device that sits between a power supply (e.g. a wall outlet) and a device (e.g. a computer) to prevent undesired features of the power source (outages, sags, surges, bad harmonics, etc.) from the supply from adversely affecting the performance of the device. A UPS traditionally can perform the following functions:  Absorb relatively small power surges.  Smooth out noisy power sources.  Continue to provide power to equipment during line sags.  Provide power for some time after a blackout has occurred. In addition, some UPS or UPS/software combinations provide the following functions:  Automatic shutdown of equipment during long power outages.  Monitoring and logging of the status of the power supply.  Display the Voltage/Current draw of the equipment.  Restart equipment after a long power outage.  Display the voltage currently on the line.  Provide alarms on certain error conditions.  Provide short circuit protection.

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Remedial Class Notes There are two basic types of UPS in modern use. The first, known as 'Off-line', passes through incoming mains power to the output sockets while the supply is good. It monitors the line constantly for a major voltage drop that signifies power failure. It then switches on it's inverter (the part that produces output alternating current from it's battery) and supplies output power until the mains voltage has been restored and is stable for a period of time. There is by definition a momentary power loss during switchover, but typically of around five milliseconds, which is insignificant to most loads. According to how much you pay for your UPS, you may get some conditioning of the mains power that is passed through under normal conditions, and you may get a genuine sine-wave output as opposed to the square-wave or trapezoidal wave that you will find on the cheaper products. The second type is known as an 'On-line' design because it's inverter is 'on-line' permanently. In this design, all the incoming power is always converted to direct current, which both tops up the batteries and feeds the inverter. The inverter is constantly producing fresh alternating current to supply the load. When the mains goes off, the batteries are still holding up the incoming DC supply to the inverter, so the load continues to be supplied with absolutely no break whatsoever. The inverter is a constant-duty inverter, so this costs a little more. In any reputable on-line UPS, there is also a fail-safe mechanism known as a 'Static Bypass' which on detecting failure in the inverter will throw the load on the mercy of the mains supply, rather than letting it drop altogether. This design inherently cleans the supply by virtue of reducing it to DC, then reconverting it to fresh AC. UPSs above 5KVA in size are almost universally on-line in design. It is difficult to produce an on-line economically below around 600VA, so most UPSs below this size are off-line. Better UPSs of both designs will crop high incoming voltages and step-up low incoming voltages without resorting to battery. When these are off-line units they are called 'line-interactive' devices - they are nonetheless fundamentally off-line devices. Almost all UPSs in their standard form will provide between five and ten minutes supply at full load. As a very rough estimate you can say that they will usually supply ten to twenty minutes supply at half load. Some UPS have a facility for extended batteries. Most on-line do, most off-line don't, but that's very general and you'll find both which can support extended batteries. When considering UPS that support extra batteries, look

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Remedial Class Notes for extension battery cabinets that incorporate battery chargers, otherwise you get a small charger that can't cope properly with a vast battery bank. At a certain point, depending on manufacturer and size, you'll find it becomes more cost-effective to revert to a 10-minute UPS and a generator fitted with mains-failure autostart. This then gives you an effectively unlimited run time.

CHECK YOUR PROGRESS 1. The primary storage unit has: a) Faster access time b) Smaller storage capacity c) Higher cost per bit of storage d) All the above 2. The performance of the CPU may be increased by providing a small memory known as: a) speed buffer b) cache memory c) both and b d) neither a and b 3. The disadvantage of magnetic tape as secondary storage device is : a) no direct access to data b) no direct verification of data c) dirty atmosphere affects the tape recording errors d) all the above 4. Pick up the hard disk from the following: a) magnetic disk b) magnetic tape c) punched paper tape d) all the above 5. Pick up the incorrect statement from the following magnetic disk is advantages compared to magnetic tape: 52

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Remedial Class Notes a) Less vulnerable to damage from dust. b) Higher transfer rate of data c) Sequential processing is faster d) None of the above State whether the following statements are correct: 1. The amount of data that can be stored in the storage unit is called the storage capacity. 2. The small storage areas in the storage are called location. 3. Primary storage is generally refereed to as RAM 4. The information stored inside a ROM gets lost when the power supply is switched off 5. In sequential access device, access time for all locations is same 6. Magnetic disk and magnetic drum are typical sequential access storage devices 7. Magnetic tape is the most suitable storage media for random access secondary storage 8. Floppy disks are popular external storage media used with small computers 9. Each character is represented on a column by a set of holes punched in various rows 10. Winchester disks are permanently housed in sealed, contamination-free containers. Answers: I 1(a) 2(c)

3(d)

II

1)True

2)True

3)True

4)False

5)False

6)False

7)False

8)True

9)True

10)True

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4(a)

5(c)

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Remedial Class Notes

NETWORKS AND MULTIMEDIA STRUCTURE 6.0 Introduction 6.1 Objectives 6.2 Local Area Network (LAN) 6.3 Multimedia 6.4 Client Server Paradigm 6.5 Modem 6.6 Check your progress

Introduction This deals with communication between different computers .Computer networking (connecting computers) allows for sharing of resources such as data and peripheral devices. Several topologies of computer networks is also presented. In a networked computer system, with programs distributed a model called client/server model provided for a convenient way for programs to interact. The client /server paradigm of the different servers is also examined. Communication device that permits connection of digital data to an existing telephone line is referred to as MODEM.

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Remedial Class Notes

Objectives •

To understand how resources (data and peripherals ) can be shared by

networking •

To understand how different services can be provided through

client/server approach •

To show how the digital and the analog worlds can be bridged through

MODEM •

How multimedia kit adds multimedia capabilities to a compute

LOCAL AREA NETWORK (LAN) LAN is a group of computers and associated devices that share a common communications line and typically show the resources of a single processor or server within a small geographic are (for example, within an office building), Usually, the server has applications and data storage that are shared in common by multiple computer users. A local area network may serve as few as two or three users ( for example, in a home network) or many as thousands of users ( for example, in an FEEI network). If you have two or more people that routinely need to easily share information and resources you are a candidate to install a LAN, Although LAN’s add a level of complexity to an office computer environment, the payback in productivity can make it well worth the effort. Simply put, a LAN allows you to share resources, Instead of attaching a printer to each machine in your office, across a LAN you can share a single printer, Files that everyone in the office needs to access frequently can be kept on the central disk drive, and a backup routine can be implemented to ensure that these central files can be retrieved in case of trouble, with the appropriate software, a single internet connection can be shared by all machines on the LAN to gain access to email and the Web, LAN’s can reduce the amount of money you spend on extra equipment and associated costs, and can help improve the way people in your office use and share information.

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NETWORK TOPOLOGY: The specific physical, i.e., real, or logical, i.e., virtual, arrangement of the elements of a network. The common types of network topology are 1.

Bus topology: A network topology in which all nodes, i.e., stations are connected together by a single bus.

2.

Fully connected topology: A network topology in which there is a direct path (branch) between any to nodes. Note: In a fully connected network with n nodes, there are n (n-1)/2 direct paths.

3.

Mesh topology: A network topology in which there are at least two nodes with two or more paths between them.

4.

Ring topology: A network topology in which every node has exactly two branches connected to it.

5.

Star topology: A network topology in which peripheral nodes are connected to a central node, which rebroadcasts all transmissions received from any peripheral node to all peripheral nodes on the network, including the originating node. Note1: All peripherals nodes may thus communicate with all others i.e., channel, linking any peripheral node to the central node only. Note2: The failure of a transmission line, i.e., channel, linking any peripheral node to the central node will result in the isolation of that peripheral node from all others. Note3: If the star central node is passive, the originating node must be able to tolerate the reception of an echo of its own transmission, delayed by the two-way transmission time

6.

Tree topology: A network topology that, from a purely topologic viewpoint, resembles an interconnection of star networks in that individual peripheral nodes are required to transmit to and receive from one other node only, toward a central node, and are not required to act as repeaters or regenerators.

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Remedial Class Notes

The main local area network technologies are:  Ethernet  Token ring  Attached Resource Computer Network  Fiber Distributed-Data Interface (Fiber Distributed Data Interface) Typically, a suite of application programs can be kept on the LAN server, Users who an application need frequently can download it once and then run it from their local hard disk. Users can order printing and other services as needed through applications run on the LAN server. A user can share files with others at the LAN server, read and write access is maintained by a LAN administrator.

Ethernet: Ethernet is the most widely-installed local area network (LAN) technology. Specified in a standard, IEEE 802.3, Ethernet was originally developed by Xerox and then developed further by Xerox, DE C, and Intel. An Ethernet LAN typically uses coaxial cable or special grades of twisted pair wires. The most commonly installed Ethernet system are called 10base-T and provided transmission speeds up to 10 MBPS. Devices are connected to the cable and compete for access using a Carrier Sense Multiple Access with Collision Detection (CSMA/CD) protocol.

Token ring: A token ring network is a local area network (LAN) in which all computers are connected in a ring or star topology and a binary digit-or token-passing scheme is used in order to prevent the collision of data between two computers that want to send messages at the same time. The token ring protocol is the second most widely used protocol on local area networks after Ethernet. The IBM Token Ring protocol led to a standard version specified as IEEE 802.5. Both protocols are used and are very similar. The IEEE 802.5 token ring technology provides for data transfer rates of either 4 or 16 megabits per second. Very briefly, here is how it works: 57

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Remedial Class Notes Empty information frames are continuously circulate on the ring. When a computer has a message to send, it inserts a token in an empty frame ( this may consist of simply changing a 0 to a 1 in the token bit part of the frame) and inserts a message and a destination identifier in the frame. The frame is then examined by each successive workstation. If the workstation sees that it is the destination for the message, it copies the message from the frame and changes the token back to 0. When the frame gets back to the originator, it sees that the token has been changed to 0 and that the message has been copied and received. It removes the message from the frame. The frame continues to circulate as an “empty” frame, ready to be taken by a workstation when it has a message to send. The token scheme can also be used with bus topology LANs The standard for the token ring protocol is Institute of Electrical and Electronics Engineers (IEEE) 802.5. The Fiber Distributed –Data Interface (FDDI) also uses a token ring protocol.

Multimedia A package of hardware and software that adds multimedia capabilities to a computer. Typically a multimedia kit includes a CD-ROM or DVD player, a soundcard, speakers, and a bundle of CD-ROMs. To play a multimedia CD-ROM disc you need to have a suitable computer and a CDROM drive. Nearly all latest computers will have built-in CD-ROM drive. You can buy an external drive for as little as Rs2,500. CD-ROM is very flexible, and all the material is stored in digital form. That is, the text, pictures, sound and animation. These are called assets and once they are created it is very simple to use them in different situations and in different multimedia products. Essentially the same assets can be used to produce point-of-sale material, a training package or a corporate presentation. Many of the assets can be also made available on the Internet. Multimedia is increasingly used in catalogue and training packages and has already established itself as an important medium that is growing at quite a pace. It will certainly replace a lot of written material in the next few years. Whether it will eventually replace books only time will tell.

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Remedial Class Notes Multimedia is one of the most powerful ways to get your message across. The opportunities are many; point-of-sale material, service manuals, training packages, for staff or franchisees, direct mail packages, a new product launch, a product catalogue or an annual report-presentations of all kinds. Multimedia is much easier than a video to update. The new information can be incorporated very easily. For example old product lines can be dropped and new added. It is ideal in toady's changing markets.

CLIENT / SERVER PARADIGM Client/Server describes the relationship between two computer programs in which one program, the client, makes a service request from another program, the sever, which fulfills the request. Although the client/server can run on a single computer, it is an important idea in a network. In a network, the client/server model provides a convenient way to interconnect programs that are distributed efficiently across different locations. Computer transactions using the client/server model are very common. For example, to check your bank account from your computer, a client program in your computer forward the request to its own client program that sends a request to a data base server at another bank computer to retrieve your account balance. The balance is returned back to the bank data client, which in turn serves it back to the client in your personal computer, which displays the information for you.

The client/server model has become one of the central ideas of network computing. Most business applications being written today use the client/server model. So does the Internet’s main program, TCP/IP. In marketing, the term has been used to distinguish distributed computing by smaller dispersed computers from the “monolithic” centralized computing of mainframe computers. But this distinction has largely disappeared as mainframes and their applications have also turned to the client/server model and become part of network computing. In the usual client/server model, one server, sometimes called a daemon, is activated and awaits client requests. Typically, multiple client programs share the services of a common server program. Both client programs and server programs are often part of a larger program or application. Relative to the Internet, your Web browser is a client program that requests services (the sending of Web pages or files) from a Web server (which technically is called a Hypertext Transport Protocol or Hypertext Transfer 59

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Remedial Class Notes Protocol server) in another computer somewhere on the Internet. Similarly, your computer with TCP/IP installed allows you to make client requests for files from File Transfer Protocol servers in other computers on the Internet. Other program relationship models included master/slave, with one program being in charge of all other programs, and peer-to-peer, with either of two programs able to initiate a transaction.

Server Process: A server process (program) fulfills the client request by performing the task requested. Server programs generally receive requests from client programs, execute database retrieval and updates, and manage data integrity and dispatch responses to client requests. Sometimes server programs execute common or complex business logic. The server-based process “may” run on another machine on the network. This server could be the host operating system or network file server; the server is then provided both file system services and application services. Or in some cases, another desktop machine provides the application services. The server process acts as a software engine that manages shared resources such as databases, printers, communication links or high powered-processors. The server process performs the back-end tasks that are common to similar applications.

Client Process: The client is a process (program) that sends a message to a server process (program), requesting that the server perform a task (service). Client programs usually manage the user-interface portion of the application, validate data entered by the user, dispatch requests to server programs, and sometimes execute business logic. The client-based process is the front-end of the application that the user sees and interacts with. The client process contains solution-specific logic and provides the interface between the user and the rest of the application system. The client process also manages the local resources that the user interacts with such as the monitor, keyboard, workstation CPU and peripherals. One of the key elements of a client workstation is the graphical user interface (GUI). Normally a part of operating system i.e. the window manager detects user actions, manages the windows on the display and displays the data in. The basic characteristics of client/server architecture are 1) Combination of a client or front-end portion that interacts with the user, and a server or back-end portion that interacts with the shared resource. The 60

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Remedial Class Notes client process contains solution-specific logic and provides the interface between the user and the rest of the application system. The server process acts as a software engine that manages shared resources such as databases, printers, modems, or high powered processors 2) The front-end task and back-end task have fundamentally different requirements for computing resources such as processor speeds, memory, disk speeds and capacities, and input/output devices. 3) The environment is typically heterogeneous and multivendor.

The

hardware platform and operating system of client and server are not usually the same. Client and server processes communicate though a well-defined set of standard application program interfaces (API’s) and RPC’s. 4) An important characteristic of client-server systems is scalability. They can be scaled horizontally or vertically. Horizontal scaling means adding or removing client workstations with only a slight performance impact. Vertical scaling means migrating to a larger and faster server machine or multiservers. The different types of servers are, the simplest form of servers are disk servers and file servers. With a file server, the client passes requests for files or file records over a network to the file server. This form of data service requires large bandwidth and can slow a network with many users down considerably. Traditional LAN computing allows users to share resources, such as data files and peripheral devices, by moving them from standalone PC’s onto a Networked File Server(NFS). The more advanced form of servers are database servers, transaction server and application servers( Orfali and Harkey 1992). In database servers, clients passes SQL ( Structured Query Language) requests as messages to the server and the results of the query are returned over the network. The code that processes the SQL request and the data resides on the server allowing it to use its own processing power to find the requested data, rather than pass all the records back to a client and let it find its own data as was the case for the file server. In transaction servers, clients invoke remote procedures that reside on servers which also contains an SQL database engine. There are procedural statements on the server to execute a group of SQL statements ( transactions) which either all succeed or fail as a unit. The applications based on transaction servers are called On-line Transaction Processing (OLTP) and tend to be mission-critical applications which require 1-3 second response time, 100% of the time and require tight controls over the security and integrity of the 61

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Remedial Class Notes database. The communication overhead in this approach is kept to a minimum as the exchange typically consists of a single request/reply (as opposed to multiple SQL statements in database servers). Application servers are not necessarily database centered but are used to server user needs, such as download capabilities from Dow Jones or regulating a electronic mail process. Basing resources on a server allows users to share data, while security and management services, which are also based in the server, ensure data integrity and security.

MODEM The word MODEM is an acronym for Modulator – Demodulator, Modems accept digital data supplied by the local PC, and convert it to a modulated analog wave form that can be transmitted over a normal analog phone line. And conversely, modems also accept a modulated analog wave from the telephone line convert it to a digital form, and pass it on to the local PC. A 28,800 or 33,600 BPS modem can send data over a phone line up to fourteen times faster than a 2400 BPS modem, and a 56k modem over twenty times faster couple this with the built-in data compression ability of modern high speed modems which will compress ordinary text data by about 2:1, and some types of data by up to 4:1, and you can see that throughput can be 25 to 50 times greater (or more!) than for a 2400 BPS modem. This tremendous increase in speed can dramatically decrease your online time and your phone charges, and makes it feasible to transfer graphics screens such as WWW pages in time acceptable to most users. CD is an acronym for compact disc. There are four main types of compact disc formats; CD Audio CD-ROM (Compact Disc-Read only memory) CD-I (Compact Disc-Interactive) and CD-RAM/XA (CD-ROM Extended Architecture) A CD is a fairly simple piece of plastic, about 1.2 millimeters thick, most of a CD consists of an injection-molded piece of clear polycarbonate plastic. During manufacturing, this plastic is impressed with microscopic bumps arranged as a single, continuous, extremely long spiral track of data. We will return to the bumps in a 62

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Remedial Class Notes moment. Once the clear piece of polycarbonate is formed, a thin, reflective aluminum layer is sputtered onto the disc, covering the bumps. Then a thin acrylic layer is sprayed over the aluminum to protect it. The label s then printed on to the acrylic. A CD has a single spiral track of data, circling from the inside of the disc to the outside. The fact that the spiral track starts at the centre means that the CD can be smaller than 12 centimeters if desired, and in fact there are now plastic baseball cards and business cards that you can put in a CD player. CD business cards hold about 2 megabytes of data before the size and shape of the card cuts off the spiral. CD-ROM: The compact disk read only memory is an optical disk memory device. It is a read-only storage medium. It is a cheaper storage medium that stores upto 650MB of data. A CD-ROM is similar to that of audio CD in construction it is a plastic disk of about 120 mm diameter, 1.2 inch thick and has a central hold of 15 mm diameter. Data in a CD-ROM is in the form of pits and lands arranged in a continuo spiral that starts at the outer edge and winds inward to the centre. The speed with which CD-ROM rotates is constantly varies, so that at any radial position of detector, the track has same speed. The advantages of CD-ROM’s are its high storage capacity, mass copy of information stored, removable from the computer etc.. The main disadvantage is longer access time as compared to that of a magnetic hard disk. Data can not be written into it because it is a read only memory. It is suitable only for storing information that need not be changed.

CHECK YOUR PROGRESS 1. What is a LAN? 2. What are the advantages of LAN? 3. What are the different LAN topologies ? explain briefly 4. What are the different LAN technologies ? explain briefly 5. What are the different components of Multimedia Kit? 6. Explain CDROM briefly 7. What are the basic characteristics of client/server paradigm? 8. What is a client process? 9. What is a server process? 63

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Remedial Class Notes 10. What does a MODEM stands for? 11. What is the use of MODEM? 12. What is a file server?

Prep. By MOHAMMAD DANISH (Lecturer, CSE Deptt.)

Al-Falah School of Engineering & Technology, Dhauj, Faridabad-121001

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